The cylinder of a known threshing unit of an axial grain combine harvester is arranged longitudinally and performs threshing of the feed material and its translation motion over the concave surface along a helical pathway. The threshing action is effected due to combined impact and rubbing effects produced by the cylinder working members and the concave bars on the crop material being threshed.
Lighter operating duties of the thresher unit featuring the longitudinal cylinder arrangement and substitution of the rubbing action for the impact one make it possible to considerably reduce the degree of grain damage which of grain and seeds and prolonging the storage period of bread grain.
However, the threshing unit of an axial combine harvester, with longitudinally arranged cylinder, apart from the aforesaid advantages, suffer from such a characteristic disadvantage as a one-sided displacement, with respect to the harvester longitudinal axis, of the crop material that has been threshed and passed through the concave, with the result that the cleaning mechanism is charged but nonuniformly uniformly as for width. This in turn lead to grain losses in the course of cleaning and affects adversely the total throughput capacity of the combine harvester. The aforesaid disadvantage stems from the fact that the material being threshed, while running through a helical pathway over the threshing zone, is subjected to repeated effect of the cylinder working members and of the concave bars, the degree of this effect being variable and depending upon the amount of the cylinder-to-concave (or threshing) clearance. Intensity of passing the crop material through the free cross-sectional area of the concave is also variable. It is due to the amount of threshing clearance diminishing towards the exit end of the machine that the traverse speed of the material being threshed over the concave is increased. Thus, the layer of the crop material being handled is spread under the effect of centrifugal forces, which contributes to separation of the material through the concave. As a result of a relative movement of the compacting layers of the crop material in a narrowing threshing clearance and of its active interaction with the concave bars, the threshing and separation process at the concave outlet is intensified. Besides, the crop material separated through the concave by virtue of centrifugal forces, is subjected to the effect of the two differently directed forces, that is, the gravitational force and a force tangential to the traversing pathway of the material being threshed along a circle arc. Non uniformly spread crop material separated through the concave results in an inadequate loading of the cleaning mechanism riddle, which impairs the operation of this mechanism and reduces the total throughput capacity of the combine harvester. Apart from all the aforesaid, when the material being threshed is moving through the threshing clearance, the material is in a compacted state throughout the concave length, which impedes separation of the threshed crop material through the concave and affects the threshing capability of the cylinder working members.
Known in the art is an axial grain combine harvester (cf. U.S. Pat. No. 3,982,549, Cl.AO1F 12/20), wherein the threshing unit comprises a rotary cylinder arranged along the direction of travel of the combine harvester and accommodated in a stationary cylindrical casing whose top portion is provided with helical guide ribs located on the casing internal surface, while the bottom portion of the casing situated in the threshing zone is provided with a change concave.
A disadvantage inherent in the aforedescribed threshing unit resides in too a low threshing capability of the concave. Due to the fact that the material being threshed is in a compacted state throughout the length of concave arc, separation of the threshed crop material through the concave is impeded and, accordingly, the threshing capability of the cylinder working members is affected adversely. Besides, throughput capacity of the threshing unit is badly affected due to too a small angle of drum-to-concave contact. Moreover, the one-sided displacement, with reference to the longitudinal axis of the cylinder, of the threshed material separated through the concave and its spreading across the width of the cleaning mechanism riddle in a layer nonuniform as for thickness, which are common to axial grain combine harvesters, affects the quality of performance of the cleaning mechanism and reduces the total throughput capacity of the harvester.
With the same longitudinally arranged threshing cylinder but with the concaves contacting the cylinder at different angles, the threshing and separating efficiency and the throughput capacity of the threshing unit is higher whenever the concave contacts the cylinder at a greater angle, while intensity of separation of the crop material through the concave and uniformity of loading of the cleaning mechanism as for width depend on the amount of the threshing clearance. However, when the angle of contact of the concave with the cylinder exceeds 120.degree. the difference between the cylinder-to-concave clearances in the various concave positions, is increased to a greater extent, which affects the normal operating process proceeding in the threshing unit and involves the use of sectional concaves and a sophisticated mode of suspension and adjustment of such concaves.
One of the indispensable prerequisites of a quality operation of the cleaning mechanism both in a traditional and an axial combine harvester is a uniform feeding, as for thickness, of a layer of the crop material. A nonuniform, as for thickness, layer of the crop material that moves over the riddle working surface, fails to be blown through completely with an air stream established by the fan of the cleaning mechanism, whereby the unthreshed grain comes out of the combine harvester along with cavings, thus affectings its total throughput capacity.
Another prior-art axial grain combine harvester (cf. U.S. Pat. No. 4,177,820, AC1F 12/20) is known to comprise a threshing unit wherein the threshing cylinder along with a stationary cylindrical casing encompassing said cylinder from above and a change concave contacting the cylinder from below, is offset towards one of the vertical walls of the harvester hull in a direction opposite to the direction of the cylinder rotation. A guide baffle is provided on the opposite vertical wall of the harvester hull, said baffle being adjustable as for the angle of deflection. However, provision of one or a number of guide baffles (on both vertical walls), though contributing to withdrawal and concentration of the principal part of the threshing products separated through the concave close to the longitudinal axis of symmetry of the conveyer, but fails to provide adequate conditions for a uniform spreading of said products across the width of the cleaning mechanism riddle. Another disadvantage of said threshing unit resides in too a low threshing capability of the concave due to the fact that the material under threshing is in a contracted state throughout the length of the concave arc, which impedes separation of the threshed material, affects the threshing capability of the cylinder working members and, due to too a small angle of cylinder-to-caving contact, also the throughput capacity of the threshing unit.
Thus, the aforediscussed known constructions of threshing units is featured by a low threshing and separating capabilities and fail to provide adequate conditions for a uniform spreading of the crop material over the cleaning mechanism riddle as for thickness. Thus, the performance of the cleaning mechanism is affected badly, which results in unsatisfied loss of grain behind the grain harvester and in a reduced total throughput capacity thereof.